The present invention relates generally to printing presses and more particularly to a method and device for reducing vibrations in printing presses.
Print unit towers have significant side frame vibration while starting up and during operation. One of the major causes of side frame vibration are vibrator rolls, which move laterally so as to provide a more consistent ink coating or dampening solution to a plate cylinder. The vibrations caused by the vibrator rolls may reduce the life of the equipment and also may cause a lateral print double on the printed material, leading to poor print quality and, often, paper waste.
Prior attempts to reduce vibrator roll vibration effects include using a separate motor to drive the lateral motion of the vibrator rolls so that the torque disturbances due to vibrator oscillation can be insulated from the unit drive, or to drive the lateral motion so that vibrator phases can be adjusted relative to one another.
However, using separate motors to drive the vibrator rolls to produce the lateral motion incurs significant additional cost and complexity over the traditional technique of having the lateral and rotational motion of the vibrator rolls driven by the same drive which drives the printing cylinders.
When the lateral motion is driven by the same drive as a corresponding print cylinder, the phasing of the various vibrator rolls for different plate cylinders typically are not controlled, especially if independent motors drive the various plate cylinders. If, for example, during a circumferential registration adjustment of one plate cylinder, the phase of the various vibrator rolls changes, those vibrator rolls may cause increased vibrations, leading to the defects mentioned above.
Japanese Patent Document No. 8-276562 purports to disclose a dynamic dampener for reducing vibrations caused by a reciprocating roller. The dynamic dampener requires a separate device, which can be expensive and can be difficult to maintain.
U.K. Patent Application No. 2 180 502 purports to disclose a device for adjusting the amplitude of the axial reciprocation of ink vibrator rollers. No change in the phasing of the axial reciprocation appears to occur, and the purpose of the device does not appear to be to reduce vibrations in a printing press, but rather to vary the stroke length of the vibrator rollers.
An object of the present invention is to provide a method and device for determining vibrator stroke positions and/or dynamically adjusting phase between vibrator rolls. An alternate or additional object is to reduce vibrations in printing presses.
The present invention provides a method for identifying the lateral position of a vibrator roll geared to a plate cylinder in a printing press comprising the steps of:
sensing a reference lateral position of a vibrator roll;
setting a counter to a specific setting corresponding to the reference lateral position of the vibrator roll; and
rotating a plate cylinder, the lateral position of the vibrator roll changing as a result of the rotating, the counter changing as a function of the rotating of the plate cylinder.
The counter thus provides for instant querying of the lateral position of the vibrator roll, as the rotation of the plate cylinder varies the lateral position of the vibrator roll. The sensing of the reference position can take place at a single lateral position of the vibrator roll, for example when the vibrator roll reaches a full extension of a vibrator stroke position.
Preferably, the counter is reset to zero each time the vibrator roll reaches a full extension of a vibrator stroke position.
Preferably, a reference lateral position of a second vibrator roll of an opposing print couple is sensed, a second counter is set to a second specific setting corresponding to the reference lateral position of the second vibrator roll, and a second plate cylinder is rotated. The lateral position of the second vibrator roll changes as a result of the rotating of the second plate cylinder, and the second counter changes as a function of the rotating of the second plate cylinder.
Depending upon the desired phase relationship between the first and second vibrator rolls (for example 180 degrees out of phase), the vibrator roll positions can then adjusted by rotating of one or both plate cylinders, as described for example in the method and device of U.S. Ser. No. 09/727,994.
Preferably, the counter values of the opposite print couples are read at an same instant in time, i.e. xe2x80x9cfrozenxe2x80x9d, so that an accurate relationship between the two print couples is established.
Each rotation of a plate cylinder alters the phase of the vibrator roll, and thus if one plate cylinder is rotated 360 degrees while the other plate cylinder is not moved, the phases between the two vibrator rolls can be altered without affecting the register. The amount of phase change in the vibrator roll position per single plate cylinder rotation is referred to herein as the xe2x80x9cphase per plate revolutionxe2x80x9d or number of degrees ND.
If the opposing vibrator rolls are out of the desired phase relationship by an amount equal or almost equal to ND, one of the opposing plate cylinders can be advanced while the other remains stationary.
However, in some presses the amount of vibration caused by a single deviation by the number of degrees ND is not significant to print quality. The correction of the desired phase relationship then can be delayed until opposing rolls are out of the desired phase relationship by an amount equal to or almost equal to 2*ND. At that point, one of the plate cylinders can be advanced one revolution, and the opposing plate cylinder retarded.
The present invention also provides a method for setting the proper register and vibrations of a printing press comprising the steps of:
determining a good printed register position of a first set of opposing plate cylinders in a first color printing unit of a printing press and of a second set of opposing plate cylinders in a second color printing units of the printing press;
removing the first set of opposing plate cylinders from impression;
removing the second set of opposing plate cylinders from impression;
pulling the web through the first and second color printing units using a nip;
sending a last good printed register command to a controller to adjust the register of the first and second sets of opposing plate cylinders to the good printed register position; and
determining vibrator stroke positions in the first and second printing units.
Preferably, the determining step is performed while the first and second set of plate cylinders are off impression.
The vibrator positions then may be altered by rotating the one or more of the plate cylinders so as to obtain the desired vibrator phase relationship.
The present invention also provides a device for identifying a vibrator roll stroke position with respect to a plate cylinder in a printing press comprising:
a sensor sensing a lateral position of a vibrator roll;
an incremental encoder for sensing rotation of a plate cylinder;
a counter for counting an output of the incremental encoder; and
a controller for rotating the plate cylinder, the controller receiving inputs from the sensor and the counter.
Preferably, the controller resets the counter upon receiving a sensor signal from the sensor.
The present invention also provides a printing press comprising:
a first color print unit including first opposing plate cylinders, vibrator rolls, and first sensors for sensing lateral positions of the vibrator rolls;
a second color print unit including second opposing plate cylinders, second vibrator rolls and second sensors for sensing lateral positions of the second vibrator rolls; and
a controller for removing the first and second plate cylinders from impression, the controller receiving inputs from the first sensors and the second sensors, and the controller capable of revolving at least one plate cylinder of the first and second opposing plate cylinders as a function of the inputs.
Preferably, the controller can set a last good print position of the plate cylinders when the cylinders are off impression.